how do I know how much alc. content my beer will have before i get the ingrediants? example I brewed up 10 pounds of light extract for a 4 gal. batch. how much alc. should i be expecting? is there a formula?

Before I got BeerTools Pro, I used to estimate my %ABV by subtracting my FG from my OG and multiplying that number by 0.131. For an all extract beer you could probably assume about 75% attenuation and 46 points per pound per gallon contribution to the OG from the extract.

10# x 46 ppppg ÷ 4 gallons x 0.75 attenuation x 0.131 = 11.3% ABV

A beer that big will probably be a challenge for the yeast to ferment completely, so you might not get normal attenuation and the ABV might be a bit lower.